The invention relates to a filter having at least two filter elements which are arranged in an axially successive manner in a common filter cartridge and which, in particular, form a fine filter and a coarse filter for filtering contaminated liquids.
A dual filter of this type is known from European Patent Document EP 0 558 828 B1, in which a coil spring is situated between the fine filter and the coarse filter, which are both axially successively arranged in a filter cartridge housing. This coil spring presses the fine filter against the housing lid in order to seal off their connection with respect to one another. By means of another coil spring, the coarse filter is supported against the housing floor and, against the force of the first coil spring, is sealingly pressed against the fine filter.
Although, it is possible in this manner to arrange two, possibly different filter elements in a filter cartridge, as a result of the large number of individual components to be combined during the assembly operation, the assembly of the filter requires high expenditures and is susceptible to errors.
It is therefore an object of the invention to provide a filter having at least two filter elements which can be assembled at low cost without disturbances during the final assembly and which operates in a reliable manner.
This object is achieved by means of connecting devices, by which the filter elements can be directly connected with one another to form a structural unit to be arranged in the filter cartridge. During the final assembly, this results in the important advantage that only the structural unit consisting of the filter elements must still be inserted into the housing of the filter cartridge, while according to the mentioned prior art at least four parts had to be inserted. The final assembly takes place much more rapidly and faults, which otherwise may result in rejects and high-cost repair work, can largely be avoided. A fitting or positioning of the filter elements with respect to one another is automatically achieved during the final assembly. The operating step of connecting the filter elements by means of connecting devices to form a structural unit can preferably take place directly after the production of the filter elements and of the connecting devices, so that the finished structural units can be handled more easily than the individual filter elements. The connecting devices are advantageously constructed such that the connection can be established in a simple manner and can occur at least partly automatically.
For each connection of two filter elements, the connecting devices can be provided on only one or, as an alternative, on both filter elements. Furthermore, it is possible to provide one connecting device for one connection respectively between two filter elements, or a single connecting element for all filter elements installed in the filter. Particularly preferably, the connecting devices are provided in the area of the connection point between the filter elements, particularly fixedly mounted on one filter element and releasably mounted on the other filter element. In this manner, a precisely defined assembly and disassembly of the structural unit can be carried out because the sequence of the mounting of the connecting devices of the filter elements is specified. As a result of the releasability of the connection at one point, individual filter elements can be exchanged.
In a preferred embodiment, the connecting devices consist of a synthetic resin material and connect the filter elements in a force-locking manner, preferably by means of molded-on catches. Such a connection can be closed and released without any tool. As an alternative, a connection, particularly a fixed connection, can take place by gluing or the like. Some type of threaded connection would also be conceivable.
Preferably, at least two filter elements are arranged such that the liquid can essentially flow through them in parallel. The filter elements preferably differ with respect to their degree of filtration; in particular, at least one is constructed as a fine filter element and one is constructed as a coarse filter element. The parallel arrangement permits an increased flow rate through the filter, which may mainly be advantageous in the case of different filtering stages because the fine filter (as a rule, with a lower throughput) takes over only a portion of the overall throughput so that a sufficient overall throughput is therefore assured. The fine filtering of only a portion of the liquid flow is considered to be sufficient.
At least two filter elements can be constructed in different sizes. While the cross-sectional surface is the same, they can preferably have different axial dimensions. Particularly when fine filters and coarse filters are used, this is advantageous because the fine filter can have a smaller construction in such a case.
A preferred embodiment of the invention has a dividing device for dividing the fluid flow into at least two sub-flows, particularly into a main flow and into a secondary flow, in which case, preferably a liquid flow can be divided into various sub-flows after separately passing through filter elements. A division preferably takes place into one clean liquid flow and one cleanest liquid flow respectively which differ with respect to the degree of purity. Such an arrangement will be especially advantageous if the liquid flow to be purified is to be used for different purposes which each make different demands on the purity. The dividing device can advantageously be part of the connecting devices in order to reduce the number of components.
Particularly preferably, the filter elements rest with their end faces against the connecting devices, in which case they can preferably be sealed off with respect to one another by the connecting devices or by a portion thereof. In this manner, the connecting devices additionally take over the advantageous function of sealing off the filter elements with respect to one another, which is particularly important when the liquid flow is divided into sub-flows.
In one preferred embodiment, at least one filter element is a folded paper filter, preferably a cylindrical expansion-bellows-type filter. Such a filter element can achieve a filtering in the radial direction and has a maximum of filtering surface while its volume is small.
As a main/secondary flow replaceable filter for cleaning an oil flow, preferably for an internal-combustion engine, the filter preferably is formed of two cylindrical filter elements, particularly a fine filter and a coarse filter, which by means of catches of a connecting element mounted on the fine filter, are connected with one another on the coarse filter to form a structural unit as a filter cartridge and are installed in a cup-like filter housing. Such a main/secondary flow replaceable filter is particularly suitable for a use in an internal-combustion engine, because different degrees of purity are desirable at different lubricating points of the engine. Thus, a higher purity is recommended, for example, at the valves than, for example, in the crankcase. Such a replaceable filter is simply exchanged for the old filter during an oil filter change.
Particularly advantageously, a pressure relief valve for bypassing at least one filter element can be provided in the filter, preferably in the area of a central opening of an end face of a filter element facing the bottom of the filter cartridge. Should a filter element be clogged by dirt and the minimum throughput considered necessary can no longer be achieved, a filter element can be bypassed by at least a portion of the liquid flow. This represents a type of safety function of the filter.
In addition to being contained in the claims, these and other characteristics are indicated in the specification and the drawings. The individual characteristics can be implemented separately or in the form of subcombinations in embodiments of the invention and in other fields and can represent advantageous and individually patentable embodiments for which protection is claimed here. The division of the application into individual paragraphs and intermediate headings does not limit the general validity of the information contained therein.